The National Institute of Child Health and Human Development plans to conduct a study that will recruit three groups of infants: infants who have developed early onset (less than or equal to 7 days of age) invasive GBS (Types Ia, Ib, II, and III) disease ("cases"), and two groups of infants who have not developed early onset GBS despite having been colonized shortly after birth: one group with colonization at multiple (>2) sites ("control group I") and one with colonization at fewer surface sites ("control group II"). GBS disease will be defined as an infection associated with isolation of GBS from a normally sterile site, such as cerebrospinal fluid or blood. A total of 240 cases, ca. 480 controls for control group I, and ca. 1440 controls for control group II will be recruited from participating hospitals over a period of 30 months. With the annual incidence rates varying from about 2-5/1000 live births, in different geographic areas and populations, Baylor College of Medicine is one of the participating collaborative center that is helping to meet the target goal of 240 cases within the assembly period of 30 months.